The 2-micron wavelength region is suitable for atmospheric carbon dioxide (CO2) measurements due to the existence of distinct absorption feathers for the gas at this particular wavelength. For more than 20 years, researchers at NASA Langley Research Center (LaRC) have developed several high-energy and high repetition rate 2-micron pulsed lasers. This paper will provide status and details of an airborne 2-micron triple-pulse integrated path differential absorption (IPDA) lidar. The development of this active optical remote sensing IPDA instrument is targeted for measuring both CO2 and water vapor (H2O) in the atmosphere from an airborne platform. This presentation will focus on the advancement of the 2-micron triple-pulse IPDA lidar development. Updates on the state-of-the-art triple-pulse laser transmitter will be presented including the status of seed laser locking, wavelength control, receiver telescope, detection system and data acquisition. Future plans for the IPDA lidar system for ground integration, testing and flight validation will also be presented.

Fibertek has developed an injection locked, resonantly pumped Er:YAG solid-state laser operating at 1.6 μm capable of pulse repetition rates of 1 kHz to 10 kHz for airborne methane and water differential absorption lidars. The laser is resonantly pumped with a fiber-coupled 1532 nm diode laser minimizing the quantum defect and thermal loading generating tunable single-frequency output of 1645-1646 nm with a linewidth of < 100 MHz. The frequency-doubled 1.6 μm Er:YAG laser emits wavelengths in the 822-823 nm spectrum, coincident with water vapor lines. Various cavity designs were studied and optimized for compactness and performance, with the optimal design being an injection seeded and locked five-mirror ring cavity. The laser generated 4 W of average power at pulse repetition frequencies (PRFs) of 1 kHz and 10 kHz, corresponding to 4 mJ and 400 μJ pulse energies, respectively. The 1645 nm was subsequently frequency doubled to 822.5 nm with a 600 pm tuning range covering multiple water absorption lines, with a pulse energy of 1 mJ and a pulse repetition frequency of 1 kHz. The resonator cavity was locked to the seed wavelength via a Pound Drever Hall (PDH) technique and an analog Proportional Integral Derivative (PID) Controller driving a high-bandwidth piezoelectric (PZT)-mounted cavity mirror. Two seed sources lasing on and off the methane absorption line were optically switched to tune the resonator wavelength on and off the methane absorption line between each sequential output pulse. The cavity locking servo maintained the cavity resonance for each pulse.

Developments in the remote detection of trace gases in the atmosphere using Differential Absorption Lidar have been driven largely by improvements in two key technologies: lasers and detectors. We have designed and built a narrow linewidth pulsed laser source with a well-controlled output wavelength and sufficient pulse energy to measure the concentration profile of CO2 and CH4 to a range in excess of 4km. We describe here the initial measurements of concentration profiles recorded with this instrument.
The system is built around a custom-designed Newtonian telescope with a 40cm diameter primary mirror. Laser sources and detectors attach directly to the side of the telescope allowing for flexible customization with a range of additional equipment. The instrument features an all-solid-state laser source based on an optical parametric oscillator (OPO) pumped by an YLF based diode-laser pumped solid-state laser and seeded by a tuned DFB seed. This provides a range of available wavelengths suitable for DIAL within the 1.5-1.6 m spectral region. The output of the OPO is beam expanded and transmitted coaxially from the receiver telescope. A gas cell within the laser source controls the seed wavelength and allows the wavelength to be tuned to match a specific absorption feature of the selected gas species. The source can be rapidly tuned between the on-line and off-line wavelengths to make a DIAL measurement of either CO2 or CH4
The receiver is based on an InGaAs avalanche photodetector. Whilst photodiode detectors are a low-cost solution their limited sensitivity restricts the maximum range over which a signal can be detected. The receiver signal is digitised for subsequent processing to produce a sightline concentration profile.
The instrument is mounted on a robust gimballed mount providing full directional movement within the upper hemisphere. Both static pointing and angular scan modes are available. Accurate angular position is available giving the sightline vector and supporting the interpretation of the concentration profile.
Initial measurements have been made in the planetary boundary layer above the City of Edinburgh and these will be presented and discussed. Earlier measurements demonstrated that the signal from atmospheric scatter could be detected at ranges in excess of 6km. The later measurements have shown scatter signals at greater ranges, but with increasing noise at the longer ranges. This is expected as the signal decreases with the inverse of the range whereas the noise remains effectively constant. Range resolved concentration profiles for sightline vectors lying within an angular sector have been used to create a 3D map of concentration for that volume. This will be presented and discussed.

We applied a broadband and coherent white light continuum to differential absorption lidar (DIAL) detection of H2O and O2 profiles in the troposphere. The white light continuum can be generated by focusing high intensity femtosecond laser pulses at 800 nm into a Kr gas cell covering a broad spectral range from UV to mid-IR. Thus, the use of white light continuum potentially enables the DIAL measurement of several greenhouse and/or pollutant gases simultaneously while minimizing the lead time for developing a tunable light source. In order to demonstrate such capability, here we report the lidar measurements of H2O and O2. These molecular species exhibit absorption lines in the near IR region where relatively high intensity of the white light continuum is available. The white light continuum was transmitted through the atmosphere collinearly to the axis of a receiver telescope. Backscattered light was passed through bandpass filters (H2O On: 725 and 730 nm, H2O Off: 750 nm, O2 On: 760 nm, O2 Off: 780 nm), and was detected by a photomultiplier tube. The detection wavelengths were selected consecutively by rotating the filter wheels that contain five bandpass filters with an interval of 1 minute. In addition, we propose a method for retrieving vertical profiles of H2O by considering wavelength dependence of the aerosol extinction coefficient α and backscatter coefficient β. These results show that for achieving precise retrieval of H2O distribution, one needs to reduce the effect of aerosol temporal variations by means of long-time accumulation or simultaneous detection of the On- and Off-wavelength signals.

Atmospheric carbon dioxide (CO2) is one of the major greenhouse gases in the Earth’s climate system. The CO2 concentration in the atmosphere has been significantly increased over the last 150 years, due mainly to anthropogenic activities. Comprehensive measurements of global atmospheric CO2 distributions are urgently needed to develop a more complete understanding of CO2 sources and sinks. Because of the importance of the atmospheric CO2 measurements, satellite missions with passive sensors such as GOSAT and OCO-2 have been launched, and those with active sensors like Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) using an integrated path differential absorption (IPDA) lidar are being studied. The required accuracy and precision for the column-integrated CO2 mixing ratios (XCO2) is high, within 1.0 ppm or approximately 0.26%, which calls for unbiased CO2 measurements and accurate determinations of the path length. The presence of clouds and aerosols can make the measurement complicated, especially for passive instruments. The heterogeneity generated by the surface elevation changes within the field of view of the sensors and the grid boxes of averaged values of atmospheric CO2 would also cause significant uncertainties in XCO2 estimates if the path length is not accurately known. Thus, it is required to study the cloud and aerosol distributions as well as the surface elevation variability in assessing the performance of the CO2 measurements from both active and passive instruments.
The CALIPSO lidar has acquired nearly 10 years of global measurement data. It provides a great opportunity to study the global distribution of clouds and aerosols as well as the statistics of the surface elevation variations. In this study we have analyzed multiple years of the CALIPSO Level 2 data to derive the global occurrence of aerosols and optically thin clouds. The results show that clear sky does not occur as frequently as expected. The global average occurrence is only about 8% for very clean air with columnar OD at 532 nm < 0.01. It increases to ~29% when OD < 0.1, and ~42% when OD < 0.3, which is close the clear atmospheric threshold from regular passive remote sensing instruments. This calls for a capability to make precise retrievals in the presence of relatively dense aerosols or thin clouds.
Multiple years of surface elevation data derived from the CALIPSO lidar has also been used in the assessment of surface elevation variability for passive sensor observations. It is shown that the variability of the surface elevation generally increases with increases in footprint size and surface elevation. For a footprint of 1-2 km typical for passive sensors, the mean standard deviation is 5-10 meters when elevation < 1 km and can reach 100 meters as the elevation increases. The occurrence frequency for a standard deviation < 10 m is greater than 20%, which can cause significant biases in the CO2 retrieval if the presence of the cloud and/or aerosol cannot be identified and corrected.
With ranging capability, the ASCENDS lidar system supported by NASA will reliably measure CO2 even in the presence of multiple backscatter targets (surface and transparent clouds) as shown during the experiments of recent airborne system demonstrations. However, it is very challenging for passive satellites to make reliable retrievals in the multiple-layer target case, because of the lack of path length information.

Proc. SPIE 10006, DUSTER lidar: transatlantic transport of aerosol particles from the Sahara and other sources: first results from the recently installed lidar and sunphotometer in Natal/Brazil, 1000607 (24 October 2016); doi: 10.1117/12.2241386

The lidar confederative network for monitoring optical properties of aerosol on Latin America, LALINET, faces an important challenger to cover a large area of Latin America with so few lidar systems. Currently in Brazil there are only three operative lidar systems, two operating on Southeastern region and other on North region of Brazil. Taking into accounting the large dimension of Brazilian territory there is a lack of lidar system monitoring in several regions. In 2014 Laser Environmental Application Laboratory (LEAL) at Nuclear and Energy Research Institute (IPEN) together with Federal University of Rio Grande do Norte (UFRN), have started the first efforts to install a depolarization lidar system at the city of Natal-RN (5°50'29'' S ,35°11'57'' W, 0 m asl), in the Northeast region of Brazil. This new lidar station intends to be in the future integrated to the LALINET network, and has as a first aim to detect and to identify aerosol layers from Saharan dust and biomass burning type arriving from African continent. To examine these transports it is paramount to have a temporally and spatially well resolved observational platforms, which will be able to describe with accuracy the transport patterns followed by these aerosol layers over the Atlantic. To yield a good coverage based on the previously mentioned requirements satellite-based platforms are very well suited, but unless a geostationary system is provided a reasonable temporal representativeness may not be achieved. Our current study is devoted to the first results aiming to detect and identify aerosol layers arriving over the Northeastern region of the South American continent, with a lidar and a sun-photometer recently installed in the city of Natal. Here we present the first aerosol observation results with the lidar system and the sunphotometer carried out from January through May 2016 with the indication of potential dust and other-type aerosol layers through some backscatter profiles.

This paper reports the results of campaigns carried out with a scanning lidar system in an industrial area for monitoring the spatial distribution of atmospheric aerosol. The aim of the study was to verify the possibility of applying a lidar system to identify fixed sources of aerosol emission, as well as to monitor the dispersion of the emitted plume, and the ability of the system to evaluate pertinent properties of the suspended particles, such as particle number concentration and representative particle size.

The data collection was carried out with a scanning backscatter lidar system in the biaxial mode with a three-wavelength light source, based on a commercial Nd:YAG laser, operating at 355 nm, 532 nm, and 1064 nm. The campaigns were carried out in an industrial site close to the city of Cubatao, Brazil, 23° 53’ S and 46° 25’ W, one of the largest industrial sites of the Country, comprising a steel plant, two fertilizer complexes, a cement plant and a petrochemical complex.

Backscattered light intensity plots were made from the primary data collected via 360-degree scans at 15 degree elevation. The collected data correspond to distances ranging from 200 m to 1500 m from the measurement location. The results indicate that the technique can provide valuable information on the spatial and temporal distribution of aerosol concentration in the area, which therefore can represent a valuable tool in source apportionment and to validate plume dispersion models.

In 2014 a new AECL (Airborne Elastic Cloud Lidar) lidar system was installed on-board the NRC Convair-580. AECL is a single wavelength elastic lidar which operates at 355nm and can supply vertical profiles of clouds and aerosols at high vertical and temporal resolution (1.5m and 0.05s). AECL is also equipped with a polarization channel and can provide information on particle phase (i.e. liquid or glaciated). The NRC AECL lidar was flown briefly on March 28, 2014 near Ottawa, Canada. In May of 2015 it was also deployed during the multi-week international HAIC (High Altitude Ice Crystals) – HIWC (High Ice Water Content) campaign near Cayenne, French Guinea. During the midlatitude flight near Ottawa, a convective cloud with cloud top extending to 4000 m was sampled by AECL. The on board in-situ cloud microphysics probes showed that the aircraft climbed through rain below 2 km reaching a mixedphase cloud above the melting layer and finally going through a supercooled layer. The lidar depolarization data from the AECL clearly identified the shallow supercooled layer near the cloud top and ice crystals with high depolarization ratio between the melting layer and the supercooled layer. In the regions of HIWC near Cayenne, the AECL laser beam was generally completely extinguished within the first 200 m. The lidar extinction coefficient, estimated using the Klett inversion technique and taken at 50 m above the aircraft showed a very good qualitative agreement with the measured in-situ extinction at flight level. The lidar extinction values had to be scaled by a factor of 5.88 to match the in-situ data. The discrepancies between the lidar estimated extinction and the direct measurements were explained, in part, by insufficient overlap correction and/or the error in the initial parameters used for the Klett inversion. In general, AECL showed promising initial results and in conjunction with other instrumentation, supplied valuable insight into the cloud optical and microphysical properties.

Atmospheric aerosols play very important roles in climate change and air particulate pollution. Lidars based on elastic scattering have been widely used to measure aerosol spatial distribution and to retrieve the profiles of aerosol optical properties by an assumption of the aerosol extinction-to-backscatter ratio. High Spectral Resolution Lidar (HSRL) is one of methods that can be used to measure aerosol optical properties without a-priori hypotheses. Compared to Raman lidar, HSRL has the advantage of day and night measurements and can be adapted to many kinds of carrying platforms.

Unlike ordinary elastic backscatter lidar, HSRL needs to separate the Mie signal scattered by atmospheric aerosol and the Rayleigh signal scattered by atmospheric molecules. Due to small spectral difference between Mie and Rayleigh signals, there are three difficulties: firstly, the laser source must have a narrow bandwidth, high energy and stable center wavelength; secondly, the receiver should have a very narrow spectral filter to separate aerosol scattering and molecular scattering; thirdly, the center wavelength of the receiver must be real-time locked to laser source.

In order to study the influence of system parameters on the measurement accuracy of a high spectral resolution lidar and to optimize their values, a simulation and analysis has been done and will be presented in this paper. In this paper, the system parameters including the linewidth of emission laser, the bandwidth of the Fabry–Pérot interferometric filter in the receiver and the spectral tracking accuracy between the receiver and laser are mainly analyzed. At the same time, several environmental factors have been considered, including atmospheric temperature and wind, pointing accuracy of platform, aerosol concentration range etc. A typical vertical distribution of atmospheric aerosol optical properties is considered and the received signals of high spectral channels are simulated. From the simulated signals, the aerosol optical properties are retrieved and the deviation relative to the input values is obtained. Under the conditions of given environmental factors, the relationship between system parameters of high spectral resolution lidar and relative error of retrieved aerosol optical properties is carried out.

Space-borne coherent wind lidar technique is considered as one of the most promising and appropriate remote Sensing methods for successfully measuring the whole global vector wind profile between the lower atmosphere and the middle atmosphere. Compared with other traditional methods, the space-borne coherent wind lidar has some advantages, such as, the all-day operation; many lidar systems can be integrated into the same satellite because of the light-weight and the small size, eye-safe wavelength, and being insensitive to the background light. Therefore, this coherent lidar could be widely applied into the earth climate research, disaster monitoring, numerical weather forecast, environment protection. In this paper, the 2μm space-borne coherent wind lidar system for measuring the vector wind profile is proposed. And the technical parameters about the sub-system of the coherent wind lidar are simulated and the all sub-system schemes are proposed. For sake of validating the technical parameters of the space-borne coherent wind lidar system and the optical off-axis telescope, the weak laser signal detection technique, etc. The proto-type coherent wind lidar is produced and the experiments for checking the performance of this proto-type coherent wind lidar are finished with the hard-target and the soft target, and the horizontal wind and the vertical wind profile are measured and calibrated, respectively. For this proto-type coherent wind lidar, the wavelength is 1.54μm, the pulse energy 80μJ, the pulse width 300ns, the diameter of the off-axis telescope 120mm, the single wedge for cone scanning with the 40°angle, and the two dualbalanced InGaAs detector modules are used. The experiment results are well consisted with the simulation process, and these results show that the wind profile between the vertical altitude 4km can be measured, the accuracy of the wind velocity and the wind direction are better than 1m/s and ±10°, respectively.

A mini-lidar to observe the activity of Martian atmosphere is developed. The 10cm-cube LED mini-lidar was designed to be onboard a Mars rover. The light source of the mini-lidar is a high powered LED of 385nm. LED was adopted as light source because of its toughness against circumference change and physical shock for launch. The pulsed power and the pulse repetition frequency of LED beam were designed as 0.75W (=7.5nJ/10ns) and 500kHz, respectively. Lidar echoes were caught by the specially designed Cassegrain telescope, which has the shorter telescope tube than the usual to meet the 10cm-cube size limit. The high-speed photon counter was developed to pursue to the pulse repetition frequency of the LED light. The measurement range is no shorter than 30m depending back-ground condition. Its spatial resolution was improved as 0.15m (=1ns) by this photon counter. The demonstrative experiment was conducted at large wind tunnel facility of Japan Meteorological Agency. The measurement target was smoke of glycerin particles. The smoke was flowed in the wind tunnel with wind speed of 0 – 5m. Smoke diffusion and its propagation due to the wind flow were observed by the LED mini-lidar. This result suggests that the developed lidar can pursue the structure and the motion of dust devil of >2m.

Form of sea wave is greatly affected by not just flow and depth of sea water, but also wind blowing on the sea surface. Therefore, measurement and analysis of sea wave motion is of assistance for control and operational safety of boats and ships. Generally, oceanic information is gauged by acoustic and electric wave. But these methods have not provided enough spatial and temporal resolution, and are completely out of touch with the on-site needs. Thus, the LED liar for sea wave measurement has been developed. The dynamic analysis of sea wave image measured by the LED lidar was conducted and the relationship with wind speed was evaluated.

In this report, we first present the specifications and measurement methodologies of the LED lidar. Then we describe the actual measurements of sea wave with shallow angle by using this lidar and the results of their analysis.

The development and validation of small size laser sources for space based range finding is of crucial importance to the development of miniature LIDAR devices for European space missions, particularly for planet lander probes. In this context, CENTRA-SIM is developing a passively q-switched microchip laser in the 1.5μm wavelength range. Pulses in the order of 2 ns and 100μJ were found to be suitable for range finding for small landing platforms.

Two different types of rate equation models have been found: microscopic quantities based models and macroscopic quantities based models. Based on the works of Zolotovskaya et al. and Spühler et al, we have developed a computer model that further exploits the equivalence between the two types of approaches. The simulation studies, using commercial available components allowed us to design a compact laser emitting 80μJ pulses with up to 30kW peak power and 1 to 2 ns pulse width.

We considered EAT14 Yb-Er doped glass as active medium and Co2+:MgAl2O4 as saturable absorber. The active medium is pumped by a 975nm semiconductor laser focused into a 200μm spot. Measurements on an experimental test bench to validate the numerical model were carried out. Several different combinations of, saturable absorber length and output coupling were experimented.

Joint analysis of the data on polarization laser sensing of cirrus obtained using the ground based polarization laser developed at National Research Tomsk State University (Russia, Tomsk) with the results of theoretical calculations is described. The possibility of estimation of the microstructure parameters of cirrus with a preferred orientation of ice crystals on the basis of comparison of the backscattering phase matrices obtained experimentally and calculated theoretically is discussed.

We present and examine two three-coefficient calibration functions to be used for the tropospheric temperature retrievals via the pure rotational Raman (PRR) lidar technique. These functions are the special cases of the general analytical calibration function in the PRR lidar technique. The general function special cases take into account the collisional (pressure) broadening of all individual atmospheric N2 and O2 PRR lines in varying degrees. We apply these two special cases to real lidar remote sensing data and compare nighttime temperature profiles retrieved using these calibration functions to the profiles retrieved using other known ones. The absolute statistical uncertainties of temperature retrieval are also given in an analytical form. Lidar measurements data, obtained in Tomsk (56.48° N, 85.05° E, Western Siberia, Russia) using the IMCES PRR lidar at λ = 354.67 nm on 1 April 2015, were used for the tropospheric temperature retrievals (3–12 km).

The appearance of 3D laser scanning technology has provided a new method for the acquisition of spatial 3D information. It has been widely used in the field of Surveying and Mapping Engineering with the characteristics of automatic and high precision. 3D laser scanning data processing process mainly includes the external laser data acquisition, the internal industry laser data splicing, the late 3D modeling and data integration system. For the point cloud modeling, domestic and foreign researchers have done a lot of research. Surface reconstruction technology mainly include the point shape, the triangle model, the triangle Bezier surface model, the rectangular surface model and so on, and the neural network and the Alfa shape are also used in the curved surface reconstruction. But in these methods, it is often focused on single surface fitting, automatic or manual block fitting, which ignores the model's integrity. It leads to a serious problems in the model after stitching, that is, the surfaces fitting separately is often not satisfied with the well-known geometric constraints, such as parallel, vertical, a fixed angle, or a fixed distance. However, the research on the special modeling theory such as the dimension constraint and the position constraint is not used widely. One of the traditional modeling methods adding geometric constraints is a method combing the penalty function method and the Levenberg-Marquardt algorithm (L-M algorithm), whose stability is pretty good. But in the research process, it is found that the method is greatly influenced by the initial value.

In this paper, we propose an improved method of point cloud model taking into account the geometric constraint. We first apply robust least-squares to enhance the initial value’s accuracy, and then use penalty function method to transform constrained optimization problems into unconstrained optimization problems, and finally solve the problems using the L-M algorithm. The experimental results show that the internal accuracy is improved, and it is shown that the improved method for point clouds modeling proposed by this paper outperforms the traditional point clouds modeling methods.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews